I have not seen one in person, however have seent he pics that ronmar is refering to. Have also heard a local dealer (here) discuss the possibility of add on if his cust requested it.
Aside from that.. you don't really have to see one to get proof of concept.. hyds can be penned out on paper and mocked up and be good to go.. just follow the moving oil.
Output of pump goes to input of relief valve.. working port on relief valve goes to the next item thwt would have been in line.. perhaps a QD.. etc.. exhaust port from the relief goes somewhere.. either vent to sump, or vent to ground.. some even 't' the supply line and vent to supply,, just depends on hose sizes, setup, and where you have room.. etc.
Soundguy